The field of this invention is that of pressure sensors and the invention relates more particularly to a cylinder pressure transmitter responsive to variations in pressure within a cylinder in an internal combustion engine during engine operation to provide an electrical control signal for use in regulating engine operation.
It has been proposed that variations in pressure in the cylinder in an internal combustion engine be sensed during engine operation for furnishing an electrical signal to a control computer means or the like for use in regulating engine operation to achieve improved fuel efficiency and operating performance while also reducing engine knocking. In one proposed arrangement for example, a piezoelectric ring element is disposed in a sparkplug well on an engine so that when a sparkplug is mounted in the well in an otherwise conventional manner to bear against the ring element with a selected initial force, the variations in cylinder pressure which occur during piston cycling are transmitted to the piezoelectric element as variations in force applied to the element. The element accordingly provides an electrical signal corresponding to the variations in cylinder pressure. It has been proposed that the signal be used in conjunction with crank angle sensing means to determine peak cylinder pressure and to determine high frequency variations in the cylinder pressure due to engine knocking to provide feedback to the computer means for adjusting spark advance to assure that peak cylinder pressure occurs at the optimum crank angle consistent with desired reduction in engine knock.
However, it is found that such piezoelectric pressure sensing means are difficult to mount to be reliably responsive to cylinder pressure variations during engine operation over a long service life and that they tend to provide weak, high impedance output signals which have not been suitable for use with computer control means for regulating operation of internal combustion engines in commercial automotive applications.